Zazen is a meditation we practice in Naikido Shiatsu. It relates to the concept of nothingness and involves regularly meditating so that you can clear your mind and come back to your true nature.
It is easy to practice in your daily life - just sit on the floor or a cushion in an upright position and try to clear your mind by not thinking about anything. You can start with short periods of 8 or 10 minutes. If you have troubles with calming your mind, try to focus on slow and deep breathing. Later, you can slowly extend and try up to 2 x 30 minutes, including a little tea ceremony in between the periods.